Industrial > Cabling & Infrastructure

There are two styles of fiber optic cable construction: loose tube and tight buffered. Both contain some type of strengthening member, such as aramid yarn, stainless steel wire strands, or even gel-filled sleeves. But each is designed for very different environments.

Loose tube cables, the older of the two cable types, are specifically designed for harsh outdoor environments. They protect the fiber core, cladding, and coating by enclosing everything within semi-rigid protective sleeves or tubes. In loose-tube cables that hold more than one optical fiber, each individually sleeved core is bundled loosely within an all-encompassing outer jacket.

Many loose-tube cables also have a water-resistant gel that surrounds the fibers. This gel helps protect them from moisture, so the cables are great for harsh, high-humidity environments where water or condensation can be a problem. The gel-filled tubes can expand and contract with temperature changes, too.

But gel-filled loose-tube cables are not the best choice when cable needs to be submerged or where it’s routed around multiple bends. Excess cable strain can force fibers to emerge from the gel.

Tight-buffered cables, in contrast, are optimized for indoor applications. Because they’re sturdier than loose-tube cables, they’re best suited for moderate-length LAN/WAN connections, long indoor runs, and even direct burial. Tight-buffered cables are also recommended for underwater applications.

Instead of a gel layer or sleeve to protect the fiber core, tight-buffered cables use a two-layer coating. One is plastic; the other is waterproof acrylate. The acrylate coating keeps moisture away from the cable, like the gel-filled sleeves do for loose-tube cables. But this acrylate layer is bound tightly to the plastic fiber layer, so the core is never exposed (as it can be with gel-filled cables) when the cable is bent or compressed underwater.

Tight-buffered cables are also easier to install because there’s no messy gel to clean up and they don’t require a fan-out kit for splicing or termination. You can crimp connectors directly to each fiber.

Want the best of both worlds? Try a hybrid, breakout-style fiber optic cable, which combines tight-buffered cables within a loose-tube housing.

Fiber optic cable can be damaged if pulled improperly. Broken or cracked fiber, for example, can result from pulling on the fiber core or jacket instead of the strength member. And too much tension or stress on the jacket, as well as too tight of a bend radius, can damage the fiber core. If the cable’s core is harmed, the damage can be difficult to detect.

Once the cable is pulled successfully, damage can still occur during the termination phase. Field termination can be difficult and is often done incorrectly, resulting in poor transmission. One way to eliminate field termination is to pull preterminated cable. But this can damage the cable as well because the connectors can be knocked off during the pulling process. The terminated cable may also be too bulky to fit through ducts easily. To help solve all these problems, use preterminated fiber optic cable with a pulling eye. This works best for runs up to 2000 feet (609.6 m).

The pulling eye contains a connector and a flexible, multiweave mesh-fabric gripping tube. The latched connector is attached internally to the Kevlar®, which absorbs most of the pulling tension. Additionally, the pulling eye’s mesh grips the jacket over a wide surface area, distributing any remaining pulling tension and renders it harmless. The end of the gripping tube features one of three different types of pulling eyes: swivel, flexible, or breakaway.

Swivel eyes enable the cable to go around bends without getting tangled. They also prevent twists in the pull from being transferred to the cable. A flexible eye follows the line of the pull around corners and bends, but it’s less rigid. A breakaway eye offers a swivel function but breaks if the tension is too great. We recommend using the swivel-type pulling eye.

A pulling eye enables all the fibers to be preterminated to ensure better performance. The terminated fibers are staggered inside the gripping tube to minimize the diameter of the cable. This enables the cable to be pulled through the conduit more easily.

Fiber optic cable consists of a core, cladding, coating, strengthening fibers, and cable jacket.

Core
This is the physical medium that transports optical data signals from an attached light source to a receiving device. The core is a single continuous strand of glass or plastic that’s measured (in microns) by the size of its outer diameter. The larger the core, the more light the cable can carry.

All fiber optic cable is sized according to its core’s outer diameter.

The three multimode sizes most commonly available are 50, 62.5, and 100 microns. Single-mode cores are generally less than 9 microns.

Cladding
This is a thin layer that surrounds the fiber core and serves as a boundary that contains the light waves and causes the refraction, enabling data to travel throughout the length of the fiber segment.

Coating
This is a layer of plastic that surrounds the core and cladding to reinforce the fiber core, help absorb shocks, and provide extra protection against excessive cable bends. These buffer coatings are measured in microns (µ) and can range from 250 to 900 microns.

Strengthening fibers
These components help protect the core against crushing forces and excessive tension during installation.

The materials can range from Kevlar® to wire strands to gel-filled sleeves.

Cable jacket
This is the outer layer of any cable. Most fiber optic cables have an orange jacket, although some types can have black or yellow jackets.

The background
As today’s networks expand, the demand for more bandwidth and greater distances increases. Gigabit Ethernet and the emerging 10 Gigabit Ethernet are becoming the applications of choice for current and future networking needs. Thus, there is a renewed interest in 50-micron fiber optic cable.

First used in 1976, 50-micron cable has not experienced the widespread use in North America that 62.5-micron cable has.

To support campus backbones and horizontal runs over 10-Mbps Ethernet, 62.5 fiber, introduced in 1986, was and still is the predominant fiber optic cable because it offers high bandwidth and long distance.

One reason 50-micron cable did not gain widespread use was because of the light source. Both 62.5 and 50-micron fiber cable can use either LED or laser light sources. But in the 1980s and 1990s, LED light sources were common. Since 50-micron cable has a smaller aperture, the lower power of the LED light source caused a reduction in the power budget compared to 62.5-micron cable—thus, the migration to 62.5-micron cable. At that time, laser light sources were not highly developed and were rarely used with 50-micron cable—mostly in research and technological applications.

Common ground
The cables share many characteristics. Although 50-micron fiber cable features a smaller core, which is the light-carrying portion of the fiber, both 50- and 62.5-micron cable use the same glass cladding diameter of 125 microns. Because they have the same outer diameter, they’re equally strong and are handled in the same way. In addition, both types of cable are included in the TIA/EIA 568-B.3 standards for structured cabling and connectivity.

As with 62.5-micron cable, you can use 50-micron fiber in all types of applications: Ethernet, FDDI, 155-Mbps ATM, Token Ring, Fast Ethernet, and Gigabit Ethernet. It is recommended for all premise applications: backbone, horizontal, and intrabuilding connections, and it should be considered especially for any new construction and installations. IT managers looking at the possibility of 10 Gigabit Ethernet and future scalability will get what they need with 50-micron cable.

Gaining ground
The big difference between 50-micron and 62.5-micron cable is in bandwidth. The smaller 50-micron core provides a higher 850-nm bandwidth, making it ideal for inter/intrabuilding connections. 50-micron cable features three times the bandwidth of standard 62.5-micron cable. At 850-nm, 50-micron cable is rated at 500 MHz/km over 500 meters versus 160 MHz/km for 62.5-micron cable over 220 meters.

Fiber Type: 62.5/125 µm
Minimum Bandwidth (MHz-km): 160/500
Distance at 850 nm: 220 m
Distance at 1310 nm: 500 m

Fiber Type: 50/125 µm
Minimum Bandwidth (MHz-km): 500/500
Distance at 850 nm: 500 m
Distance at 1310 nm: 500 m

As we move towards Gigabit Ethernet, the 850-nm wavelength is gaining importance along with the development of improved laser technology. Today, a lower-cost 850-nm laser, the Vertical-Cavity Surface-Emitting Laser (VCSEL), is becoming more available for networking. This is particularly important because Gigabit Ethernet specifies a laser light source.

Other differences between the two types of cable include distance and speed. The bandwidth an application needs depends on the data transmission rate. Usually, data rates are inversely proportional to distance. As the data rate (MHz) goes up, the distance that rate can be sustained goes down. So a higher fiber bandwidth enables you to transmit at a faster rate or for longer distances. In short, 50-micron cable provides longer link lengths and/or higher speeds in the 850-nm wavelength. For example, the proposed link length for 50-micron cable is 500 meters in contrast with 220 meters for 62.5-micron cable.

Migration
Standards now exist that cover the migration of 10-Mbps to 100-Mbps or 1 Gigabit Ethernet at the 850-nm wavelength. The most logical solution for upgrades lies in the connectivity hardware. The easiest way to connect the two types of fiber in a network is through a switch or other networking “box.“ It is not recommended to connect the two types of fiber directly.

Multimode, 50- and 62.5-micron cable.
Multimode cable has a large-diameter core and multiple pathways of light. It comes in two core sizes: 50-micron and 62.5-micron.

Multimode fiber optic cable can be used for most general data and voice fiber applications, such as bringing fiber to the desktop, adding segments to an existing network, and in smaller applications such as alarm systems. Both 50- and 62.5-micron cable feature the same cladding diameter of 125 microns, but 50-micron fiber cable features a smaller core (the light-carrying portion of the fiber).

Although both can be used in the same way, 50-micron cable is recommended for premise applications (backbone, horizontal, and intrabuilding connections) and should be considered for any new construction and installations. Both also use either LED or laser light sources. The big difference between the two is that 50-micron cable provides longer link lengths and/or higher speeds, particularly in the 850-nm wavelength.

Single-mode, 8–10-micron cable.
Single-mode cable has a small, 8–10-micron glass core and only one pathway of light. With only a single wavelength of light passing through its core, single-mode cable realigns the light toward the center of the core instead of simply bouncing it off the edge of the core as multimode does.

Single-mode cable provides 50 times more distance than multimode cable. Consequently, single-mode cable is typically used in long-haul network connections spread out over extended areas, including cable television and campus backbone applications. Telcos use it for connections between switching offices. Single-mode cable also provides higher bandwidth, so you can use a pair of single-mode fiber strands full-duplex for up to twice the throughput of multimode fiber.

Specification comparison:

50-/125-Micron Multimode Fiber

850-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 3.5 dB/km;
Distance: 550 m;

1300-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 1.5 dB/km;
Distance: 550 m

62.5-/125-Miron Multimode Fiber

850-nm Wavelength:
Bandwidth: 160 MHz/km;
Attenuation: 3.5 dB/km;
Distance: 220 m;

1300-nm Wavelength:
Bandwidth: 500 MHz/km;
Attenuation: 1.5 dB/km;
Distance: 500 m

8–10-Micron Single-Mode Fiber

Premise Application:
Wavelength: 1310 nm and 1550 nm;
Attenuation: 1.0 dB/km;

Outside Plant Application:
Wavelength: 1310 nm and 1550 nm;
Attenuation: 0.1 dB/km

With breakout- or fanout-style cables, the fibers are packaged individually. A breakout cable is basically several simplex cables bundled together in one jacket. Breakout cables are suitable for riser and plenum applications, and conduit runs.

This differs from distribution-style cables where several tight-buffered fibers are bundled under the same jacket.

This design of the breakout cable adds strength to the cable, although that makes it larger and more expensive than distribution-style cables.

Because each fiber is individually reinforced, you can divide the cable into individual fiber lines. This enables quick connector termination, and eliminates the need for patch panels.

Breakout cable can also be more economical because it requires much less labor to terminate.

You may want to choose a cable that has more fibers than you actually need in case of breakage during termination or for future expansion.